I want to calculate the gravitational force between a uniform rod of mass $2\,\rm kg$, length $1\,\rm m$ and a uniform sphere of mass $0.2\,\rm kg$. Distance between the sphere and the rod is $0.1\,\rm m$. The sphere is in the same line as the rod, i.e. sphere is one meter from the near end of the rod.

I thought of integrating


from $0.1$ to $1.1$ meter which does yield the correct result, but the solution in the textbook has a different procedure.

  • 1
    $\begingroup$ There's no question in your question. Are you concerned that there might be two methods to calculating a result? This is a good thing. Or are you concerned that your method might have gotten you the right answer by accident? $\endgroup$
    – BMS
    Commented Feb 26, 2014 at 7:54
  • $\begingroup$ If you want to describe the method suggested by the textbook we could comment on that, but your approach seems fine. $\endgroup$ Commented Feb 26, 2014 at 8:05

1 Answer 1


Thank you for your comments. As for the solution in the textbook, they integrated the gravitational field an then calculated the force.


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